MIXUTE STRUCTURE OF THE LOBULES. 873 



portal canals, which are tubular passages formed in the substance of the 

 gland, commencing at the transverse fissure, and branching upwards and 

 outwards from that part in all directions. Each portal canal (even the 

 smallest) contains, as shown in a longitudinal section, one principal branch 

 of the vena portae, of the hepatic artery, and of the biliary duct ; the whole 

 being invested within the larger portal canals by the areolar tissue of the 

 capsule of Glissou. 



The portal vein subdivides into branches which ramify between the lobules, 

 anastomosing freely around them, and are named interlobular veins. The 

 twigs from these penetrate the lobules at their circumference, and end in the 

 capillary network from which the iutralobular (hepatic) veins take origin. 

 Within the portal canals the branches of the portal veins receive small 

 tributaries called "vaginal veins," which return to them the blood which has 

 circulated in the capsule of Glisson, and also "vense advehentes capsulares," 

 from the fibrous coat of the liver. 



The hepatic artery terminates in three sets of branches, termed vaginal, 

 capsular, and interlobular. The vaginal branches ramify within the portal 

 canals, supplying the walls of the ducts and Glisson's capsule. The capsular 

 branches appear on the surface of the liver spread out on the fibrous sheath, 

 and are accompanied by the veins which return their blood to the portal 

 branches. The interlobular branches accompany the interlobular veins, 

 but are of much smaller diameter. It has been supposed by Kiernan, 

 Ferreiu, and Theile, that the blood which they convey is entirely taken up 

 by the portal veins before reaching the capillaries from, which the hepatic 

 veins take origin ; but the view, which has been held by other anatomists, 

 that the hepatic arteries, transmit blood directly to the capillary network 

 between the portal and hepatic veins, is supported by the experiments of 

 Chrzonszczewsky, mentioned further on. 



The capillary network is very close, and, in specimens in which it has been 

 filled with transparent injection, can be seen to be continued uninterruptedly 

 from one lobule to another. 



The distribution of the portal and hepatic veins within the lobules, as just described, 

 has suggested an explanation of the mottled aspect of the liver, an appearance which 

 formerly led to the erroneous idea of there being two substances in each lobule, one 

 darker than the other. The colour of the hepatic substance itself is pale yellow, and 

 would be uniform throughout, were it not varied according to the quantity of blood 

 contained in its different vessels. Thus, if the system of hepatic veins be congested, the 

 centre of each lobule is dark, and its margin pale : this is the common case after death, 

 and is named by Kiernan passive congestion. In what is considered an active state 

 of hepatic congestion, the dark colour extends to the portal system, across the inter- 

 lobular fissures, leaving intermediate spaces, which remain as irregular pale spots : 

 this state occurs especially in diseases of the heart. When, on the other hand, the 

 portal system is congested, which is rare, and occurs generally in children, the mar- 

 gins of the lobules are dark, and their centres pale. 



The Hepatic Cells. The principal part of the secreting substance of the 

 liver, and that which seems to form nearly the whole bulk of the lobules 

 when unprepared sections are examined with the microscope, consists of 

 nucleated cells. The hepatic cells are of a spheroidal, compressed, or poly- 

 hedral form, having a mean diameter of from T ^-g- r) th to -^i^th of an inch : 

 according to Henle some of them are only -p^^th of an inch in dia- 

 meter. They present some colour even when highly magnified, being of 

 a faint yellowish hue. They usually include a very clear bright vesicular 

 nucleus of a rounded form, within which again one or two nucleoli may be 



